This invention relates generally to plotters, and more specifically to monitoring and controlling the quality of markings on plotting media.
A typical plotter comprises a pen for producing markings on a medium in response to instructions from, for example, a computer. The medium such as paper is movable in a first direction along the X-axis and the pen on a main carriage is movable in a second direction along the Y-axis which is perpendicular to the first direction. Thus, by appropriate control of the drives for the pen and paper movement, any desired graphical representation can be produced on the medium. The writing system also typically comprises a plurality of pens, for example pens of different colors. A pen handling mechanism is provided which permits a pen to move into position on the carriage for plotting on the medium and replaces that pen by another one, for example when a different color is desired.
Writing systems such as the above-mentioned pen plotter are typically used for producing rather complex graphical representations, for example circuit layouts or construction diagrams, which are electronically stored in a computer on which they may also have been created by a user. Once the plotting of those electronically stored drawings has been initiated by a user, the plotting continues automatically and the user only has to take the completed drawing from the plotter. In practice, however, the completed drawings have not always been satisfactory. As a consequence thereof, the entire drawing generally had to be plotted again.
Thus, a considerable amount of time is wasted and the efficiency of the plotting is decreased. Usually these problems are resolved by perfecting the components of the plotter.
Despite such attempts for perfection of the writing components, writing failures may still occur.
More recently, the full color inkjet printer/plotters which have been developed comprise a plurality of inkjet pens of diverse colors. A typical color inkjet printer/plotter has four inkjet pens, one that stores black ink, and three that store colored inks, e.g., magenta, cyan and yellow. The colors from the three color pens are mixed to obtain any particular color.
The pens are typically mounted in stalls within an assembly which is mounted on the carriage of the printer/plotter. The carriage assembly positions the inkjet pens and typically holds the circuitry required for interface to the heater circuits in the inkjet pens.
Full color printing and plotting requires that the colors from the individual pens be precisely applies to the media. This requires precise alignment or the carriage assembly. Unfortunately, mechanical misalignment of the pens in conventional inkjet printer/plotters results in offsets in the X direction (in the media or paper axis) and in the Y direction (in the scan or carriage axis). This misalignment of the carriage assembly manifests as a misregistration of the print images applied by the individual pens. In addition, other misalignments may arise due to the speed of the carriage, the curvature of the platen and/or spray from the nozzles.
However, the integration of the optical and electronic components in the optical sensor, as well as positioning the optical sensor on the carriage have been complicated, expensive and to some extent imprecise in prior printers/plotters. The need for reliability and precision is even greater in recent inkjet printers/plotters which print high resolution color graphics and images, often on very large poster-size printouts.